Soil Water Potential Research Articles

Evidence for scale-dependent root-antation feedback and its role in halting the spread of a pantropical shrub into an endemic sedge.

Vegetation pattern formation is a widespread phenomenon in resource-limited environments, but the driving mechanisms are largely unconfirmed empirically. Combining results of field studies and mathematical modeling, empirical evidence for a generic pattern-formation mechanism is demonstrated with the clonal shrub Guilandina bonduc L. (hereafter Guilandina) on the Brazilian island of Trindade. The mechanism is associated with water conduction by laterally spread roots and root augmentation as the shoot grows-a crucial element in the positive feedback loop that drives spatial patterning. Assuming precipitation-dependent root-shoot relations, the model accounts for the major vegetation landscapes on Trindade Island, substantiating lateral root augmentation as the driving mechanism of Guilandina patterning. Guilandina expands into surrounding communities dominated by the Trindade endemic, Cyperus atlanticus Hemsl. (hereafter Cyperus). It appears to do so by decreasing the water potential in soils below Cyperus through its dense lateral roots, leaving behind a patchy Guilandina-only landscape. We use this system to highlight a novel form of invasion, likely to apply to many other systems where the invasive species is pattern-forming. Depending on the level of water stress, the invasion can take two distinct forms: (i) a complete invasion at low stress that culminates in a patchy Guilandina-only landscape through a spot-replication process, and (ii) an incomplete invasion at high stress that begins but does not spread, forming isolated Guilandina spots of fixed size, surrounded by bare-soil halos, in an otherwise uniform Cyperus grassland. Thus, drier climates may act selectively on pattern-forming invasive species, imposing incomplete invasion and reducing the negative effects on native species.

Effect of freeze–thaw process on heat transfer and water migration between soil water and groundwater

Understanding the mechanisms of water migration and heat transfer in frozen soil is essential for the selection of water resource management measures and determination of irrigation schemes for winters. However, the dynamics of the groundwater level and temperature caused by freezing and thawing and their impact on soil water redistribution remain unclear. In this field study, the mechanisms of water migration and heat transfer in the soil during the freeze–thaw period under the combined action of the surface temperature change (upper boundary) and groundwater level fluctuation (lower boundary) were comprehensively considered with the theory and method of heat transfer, freeze–thaw characteristic curves of soil, and water balance model. The results showed that: (1) The soil temperature distribution and groundwater temperature dynamics can be interpreted intuitively by the soil temperature gradient and accumulated heat storage. (2) The freeze–thaw characteristic curves of soil indicated that the soil temperature dynamics caused a phase transition of the soil water. This further changed the soil water potential and permeability by 1–2 magnitudes and 1–5 magnitudes, respectively, which affected the direction and quantity of water migration. (3) The water balance quantitatively revealed the controlling effect of groundwater level changes caused by freezing and thawing on soil moisture dynamics. About 20% of the ice in the frozen layer was formed by the upward recharge of the groundwater during the freezing period. In the thawing period, most of this water returned to the groundwater (84%), while the rest (16%) increased the soil water content. These results systematically explain the mechanisms of heat transfer and water migration between the soil water and the groundwater during the freeze–thaw period, providing a theoretical reference for agricultural water management in seasonally frozen regions.

Detecting and attributing the changes in baseflow in China’s Loess Plateau

Baseflow plays an important role in sustaining the ecosystem during dry seasons or in arid regions, and its spatiotemporal variations greatly influence the stability of ecosystem. Because of climate change and the revegetation project, the streamflow has been reported to significantly decrease in past decades in China’s Loess Plateau (CLP); however, the changes in streamflow components have not been fully investigated. The objective of this study is thus to detect and attribute the changes in baseflow in the CLP using data of 55 hydrological stations for 1956–1990 and 2001–2019. The geographic detector, correlation analysis and elasticity coefficient methods were employed to qualitatively and quantitively analyze the influence of various factors on baseflow. The baseflow accounts for 35%-76% of streamflow. The baseflow in 85% of hydrological stations decreased by >10%, while the baseflow index (BFI) of 82% hydrological stations showed an upward trend. Precipitation and hydrogeological condition (e.g., loess thickness) were likely to dominate the spatial heterogeneity of baseflow, while the potential evapotranspiration, population, sub-surface runoff, NDVI and soil water were responsible for the decrease in baseflow with contributions of 27%, 21%, 17%, 16% and 16%, respectively. The consistence or inconsistence between baseflow and BFI as well as their relations to environmental changes provide new insights into the changes in hydrological processes.

Above and belowground traits impacting transpiration decline during soil drying in 48 maize (Zea mays) genotypes.

Stomatal regulation allows plants to promptly respond to water stress. However, our understanding of the impact of above and belowground hydraulic traits on stomatal regulation remains incomplete. The objective of this study was to investigate how key plant hydraulic traits impact transpiration of maize during soil drying. We hypothesize that the stomatal response to soil drying is related to a loss in soil hydraulic conductivity at the root-soil interface, which in turn depends on plant hydraulic traits. We investigate the response of 48 contrasting maize (Zea mays) genotypes to soil drying, utilizing a novel phenotyping facility. In this context, we measure the relationship between leaf water potential, soil water potential, soil water content and transpiration, as well as root, rhizosphere and aboveground plant traits. Genotypes differed in their responsiveness to soil drying. The critical soil water potential at which plants started decreasing transpiration was related to a combination of above and belowground traits: genotypes with a higher maximum transpiration and plant hydraulic conductance as well as a smaller root and rhizosphere system closed stomata at less negative soil water potentials. Our results demonstrate the importance of belowground hydraulics for stomatal regulation and hence drought responsiveness during soil drying. Furthermore, this finding supports the hypothesis that stomata start to close when soil hydraulic conductivity drops at the root-soil interface.

Quantifying the drivers of ecosystem fluxes and water potential across the soil-plant-atmosphere continuum in an arid woodland

Dryland ecosystems occupy a vast swath of the terrestrial land surface and exert a sizeable impact on the cycling of carbon and water globally. These biomes are characterized by tightly coupled carbon and water cycles that respond rapidly to transient pulses in water availability. However, there exist many mechanistic uncertainties regarding the environmental drivers of, and linkages between, plant and ecosystem processes. Thus, drylands are often poorly represented in many vegetation and land surface models. An enhanced understanding of dryland ecosystem function is limited by the lack of long-term, co-located, and frequent measurements of plant and ecosystem processes. At a piñon-juniper woodland in southeastern Utah, USA, we collected a continuous dataset of meteorological conditions, soil water potential from surface to bedrock, tree water potential, and ecosystem carbon and water fluxes from eddy covariance. We found that predawn and midday tree water potential and daily ecosystem fluxes were highly sensitive to fluctuations in soil water availability, particularly in shallower layers, and that daytime variability in atmospheric drivers only loosely controlled these processes. The strong connections between shallow soil water potential, tree water potential, and ecosystem fluxes occurred because of the dominant role of precipitation pulses in driving vegetation activity, as even small pulses of moisture stimulated shallow soil water potential, tree water potential, and evapotranspiration for between 1 and 2 weeks. Carbon fluxes (net ecosystem exchange and gross primary productivity) were sensitive to precipitation pulses for longer, up to 3 weeks. Our results highlight that improved monitoring and sensing of shallow soil moisture can greatly enhance our understanding of dryland ecosystem function. A better mechanistic understanding of the impacts of precipitation pulses is also needed to improve vegetation modeling of dryland ecosystems.

Brackish water promote the ecological restoration of estuarine wetland

By taking the indoor soil column experiment as the experimental simulation object, an infiltration experiment was conducted using freshwater and brackish water with different concentrations (3-g/L, 9-g/L). The constant head or air boundary of 3 cm was set as different variables (Where the air boundary means the water surface is flush with the soil interface, and the 3 cm fixed head boundary means the water accumulation depth is 3 cm above the soil interface). By analyzing the cumulative infiltration, soil water content, wetting peak, and infiltration rate, the effects of different water and salt conditions and different boundary conditions on the infiltration process were summarized and analyzed. The results show that the infiltration rate was most favorable under the 3-g/L brackish water infiltration. Under this condition, the cumulative infiltration was the largest, the time for the soil moisture content to reach saturation was the shortest, the wetting peak first reached the bottom of the soil column, and the soil water potential changed first. The constant head condition accelerated the infiltration rate of soil water, increased the cumulative infiltration, increased the soil water content, and reduced the time for the wetting peak to reach the bottom. Compared with that in the air boundary condition, the soil water potential under the constant head infiltration condition was larger. These experimental results show that to some extent, proper concentrations of saltwater are conducive to the infiltration and circulation of soil water. The demand for water saving in agricultural irrigation is increasing, and the efficiency of agricultural irrigation can be improved by making full use of the theory of unsaturated soil infiltration. The instability and complexity of unsaturated soil is due to the presence of matrix suction, so the study of unsaturated soil has profound theoretical significance.

Revisiting Soil Water Potential: Towards a Better Understanding of Soil and Plant Interactions

Soil water potential (SWP) is vital for controlling the various biological and non-biological processes occurring through and across the soil-plant-atmosphere continuum (SPAC). Although the dynamics and mechanisms of SWP have been investigated for several decades, they are not as widely explored in ecohydrology research as soil moisture, due at least partly to the limitation of field observation methods. This limitation restricts the understanding of the responses of plant physiology and ecological processes to the SWP gradient and the ecohydrological functions of SWP dynamics in different contexts. Hence, in this work, we first briefly revisit the origin and development of the concept of SWP and then analyze the comprehensive factors that influence SWP and the improvement of SWP observation techniques at field scales, as well as strategies for developing new sensors for soil water status. We also propose views of focusing on the response characteristics of plant lateral roots, rather than taproots, to SWP dynamics, and using hormone signaling research to evaluate plant response signals to water stress. We end by providing potential challenges and insights that remain in related research, such as the limitations of the SWP evaluation methods and the future development direction of SWP data collection, management, and analysis. We also emphasize directions for the application of SWP in controlling plant pathogens and promoting the efficiency of resource acquisition by plants. In short, these reflections revisit the unique role of SWP in eco-hydrological processes, provide an update on the development of SWP research, and support the assessment of plant drought vulnerability under current and future climatic conditions.

Physiological Adaptation Mechanisms to Drought and Rewatering in Water-Saving and Drought-Resistant Rice.

Water-saving and drought-resistant rice (WDR) has high a yield potential in drought. However, the photosynthetic adaptation mechanisms of WDR to drought and rehydration have yet to be conclusively determined. Hanyou 73 (HY73, WDR) and Huanghuazhan (HHZ, drought-sensitive cultivar) rice cultivars were subjected to drought stress and rewatering when the soil water potential was -180 KPa in the booting stage. The leaf physiological characteristics were dynamically determined at 0 KPa, -30 KPa, -70 KPa, -180 KPa, the first, the fifth, and the tenth day after rewatering. It was found that the maximum net photosynthetic rate (Amax) and light saturation point were decreased under drought conditions in both cultivars. The change in dark respiration rate (Rd) in HY73 was not significant, but was markedly different in HHZ. After rewatering, the photosynthetic parameters of HY73 completely returned to the initial state, while the indices in HHZ did not recover. The antioxidant enzyme activities and osmoregulatory substance levels increased with worsening drought conditions and decreased with rewatering duration. HY73 had higher peroxidase (POD) activity as well as proline levels, and lower catalase (CAT) activity, ascorbate peroxidase (APX) activity, malondialdehyde (MDA) level, and soluble protein (SP) content during all of the assessment periods compared with HHZ. In addition, Amax was markedly negatively correlated with superoxide dismutase (SOD), POD, CAT, and SP in HY73 (p < 0.001), while in HHZ, it was negatively correlated with SOD, CAT, APX, MDA, Pro, and SP, and positively correlated with Rd (p < 0.001). These results suggest that WDR has a more simplified adaptation mechanism to protect photosynthetic apparatus from damage in drought and rehydration compared with drought-sensitive cultivars. The high POD activity and great SP content would be considered as important physiological bases to maintain high photosynthetic production potential in WDR.

A general framework for jointly modelling thermal and hydric constraints on developing eggs

Abstract Eggs are a vulnerable stage because they are sensitive to thermal and hydric conditions and yet cannot behaviourally avoid stressful environments. A general mechanistic model of egg development in natural nests requires microclimatic predictions of temperature, humidity, radiation (if above ground) and water potential (if buried in soil) to be integrated with models of heat and water exchange of the egg and the metabolism of the developmental process. Although all the required pieces for such a model now exist, they have not been integrated into a general modelling framework. We developed such an integration using NicheMapR package for mechanistic niche modelling. Specifically, we took an existing general model of egg water exchange and connected it with the microclimate model in NicheMapR to simulate nest thermal and hydric environments, including the effects of soil water potential on liquid and vapour exchange and moisture‐mediated soil thermal conductivity on heat exchange. We then used the Dynamic Energy Budget model within the ectotherm model of NicheMapR as the mechanistic engine for the developmental process, allowing the explicit computation of the dynamics of metabolic heat production and all aspects of mass exchange. We illustrate the modelling framework using existing laboratory and field data on reptiles, insects, and birds. We show that it can capture laboratory observations of water exchange and metabolic heat production and how it can be used to map potential development and water uptake under natural conditions at the continental scale. The modelling framework can be used to interpret laboratory experiments and allows strong inferences to be made about the abiotic constraints on egg development in natural nests under past, present, and future environmental change.

Comparing Model Representations of Physiological Limits on Transpiration at a Semi‐Arid Ponderosa Pine Site

AbstractMechanistic representations of biogeochemical processes in ecosystem models are rapidly advancing, requiring advancements in model evaluation approaches. Here we quantify multiple aspects of model functional performance to evaluate improved process representations in ecosystem models. We compare semi‐empirical stomatal models with hydraulic constraints against more mechanistic representations of stomatal and hydraulic functioning at a semi‐arid pine site using a suite of metrics and analytical tools. We find that models generally perform similarly under unstressed conditions, but performance diverges under atmospheric and soil drought. The more empirical models better capture synergistic information flows between soil water potential and vapor pressure deficit to transpiration, while the more mechanistic models are overly deterministic. Although models can be parameterized to yield similar functional performance, alternate parameterizations could not overcome structural model constraints that underestimate the unique information contained in soil water potential about transpiration. Additionally, both multilayer canopy and big‐leaf models were unable to capture the magnitude of canopy temperature divergence from air temperature, and we demonstrate that errors in leaf temperature can propagate to considerable error in simulated transpiration. This study demonstrates the value of merging underutilized observational data streams with emerging analytical tools to characterize ecosystem function and discriminate among model process representations.

Assessing the influence of cover crop on soil water dynamics using soil moisture measurements and hydrus‐1D simulations

AbstractWinter cover crop (CC) has the potential for improving soil physical condition; however, both improvement and depletion of soil water storage because of CC were reported depending on the soil depth and the rainfall received in a growing season. The present study used sensors to measure the soil moisture content (cm3 cm−3) and soil water potential (–cm) for a no‐till corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] system managed with and without winter CC. The sensors were installed at three soil depths (15, 30, and 45 cm) and the measurements were continued for three cash crop growing seasons (corn, 2017; soybean, 2018; and corn, 2019). The observed soil water potential (–cm) was lower (high tension) for the no cover crop (NCC) system as compared to the CC for the 45‐cm depth in 2017 and 2019, and 15‐ and 30‐cm depth in 2018. The Hydrus‐1D satisfactorily simulated the soil water potential and moisture content values for the CC and NCC systems with a coefficient of determination (R2) ranging from .58 to .93 and .57 to .92, respectively. The CC stored 12, 17, and 7% less soil water in the Ap soil layer (0–18 cm) than NCC for the day of cash crop planting for the years 2017, 2018, and 2019, respectively. However, the water input from rainfall replenished the soil moisture after the establishment of the cash crop and resulted in increased soil water storage in the CC as compared to the NCC in the Ap soil layer for the years 2018 and 2019. The present study, therefore, concluded that the use of winter CC improved soil water status for the following cash crop as compared to a NCC system.

Hydraulic performance assessment of a multi-layered landfill cover system under constant water ponding

Abstract The engineered multi-layered cover system (MLCS) is used to minimize rainwater infiltration into the wastes accommodated in near surface waste disposal facility (NSDF). It is important to assess the hydraulic performance of MLCS before deploying it in the field. For this purpose, an instrumented three-layered soil column representing MLCS was subjected to 1.5 m constant ponding head for 400 days. The variation of volumetric water content and soil water potential was monitored as a function of depth and time. The objective of the study is to understand the long-term hydraulic performance and rate of saturation of different layers of MLCS. Under constant water ponding, the time to saturation for 0.3 m in surface layer, 0.6 m in drainage layer and 1.0 m in hydraulic barrier layer was observed as 24, 223 and 262 days, respectively. The numerical analysis of the MLCS predicted comparable time duration of 25, 234 and 272 days, respectively. It was noted that the numerical simulation performed by using measured wetting hydraulic parameters matched well with the experimental observation. The importance of soil specific calibration of water content sensors to improve the accuracy of observations was demonstrated. Percentage error in the estimation of layer specific soil water storage, clearly indicates that the volumetric water content measurements using profile probe was marginally better than 5TM measurements.

Alternate wetting and drying modulated physio-biochemical attributes, grain yield, quality, and aroma volatile in fragrant rice.

Alternate wetting and drying (AWD) has been recognized as a water-saving technology in rice production systems; however, pre- and post-flowering AWD could induce changes in yield, quality and aroma biosynthesis in fragrant rice. In the present study, two fragrant rice cultivars (Guixiangzhan and Nongxiang-18) were subjected to AWD till soil water potential reached -25 to -30 kPa during vegetative stage (VS), reproductive stage (RS), and both stages (VS + RS). The AWD did not affect net photosynthesis and gas exchange significantly, while malondialdehyde (MDA), H2 O2 and electrolyte leakage (EL) were higher than in control plants. The AWD treatments variably affected soluble sugars, proline and protein accumulation as well as the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and reduced glutathione (GSH) contents. Moreover, filled grain percentage and 1000-grain weight in AWD treatments were found to be statistically similar (p > 0.05) to control, except grains panicle-1 under AWD-VS + RS that was reduced by 11% and 14% for Guixiangzhan and Nongxiang-18, respectively. On average, yield and related attributes in Guixiangzhan remained higher than in Nongxiang-18. In addition, the grain aroma volatile (2-acetyl-1-pyrroline, 2-AP) content increased by 8.79%, 14.45%, and 6.87% and 7.95%, 14.02%, and 5.04% under AWD-VS, AWD-RS, and AWD-VS + RS treatments, for Guixiangzhan and Nongxiang-18, respectively. Overall, AWD treatments, either at VS or RS, could promote rice aroma in terms of accumulation of 2AP, which might be linked with enhanced endogenous proline contents (a precursor for 2AP biosynthesis) without any severe consequences on rice yield and quality.

DROUGHT EFFECTS ON PHYSIOLOGICAL PARAMETERS OF DURUM AND BREAD WHEAT

The present research discusses the dynamics of changes in the surface of assimilation organs of different durum and bread wheat genotypes differing in the maturation period due to drought conditions. Under drought conditions, the soil water potential decreases, and in the later stages of the plants, the turgor pressure decreases, the stomata close, and a sharp decrease in photosynthetic activities. The situation creates stress in the crop plant, and various biochemical, physiological, and molecular reactions arise to overcome and protect itself from stress, allowing the plant to develop resistant mechanisms to adapt to the external environment. The existent research aimed to determine drought effects on assimilating surface areas and productivity traits of durum and bread wheat genotypes differing in their maturation periods grown under various climatic and soil conditions, with the comparison of the physiological indices. The experiments proceeded on wheat genotypes with contrasting maturation periods (early, medium, and late) during 2021–2022 at the Research Institute of Crop Husbandry, Absheron, Azerbaijan. The assimilating surface area of various organs underwent comparative studies in two durum (Garagylchyg-2 and Alinja-84) and two bread wheat (Nurlu-99 and Gobustan) cultivars under normal water supply and drought conditions. Post anthesis water stress caused a 34% and 27% reduction in grain yield and 1000-grain weight, respectively, while no significant effect on the grains per spike and spikes per m2. The averages of grain yield and 1000-grain weight of different wheat cultivars in the controlled condition showed 696±36 g/m2 and 43.1±0.8 g/m2, respectively, while under water-stress conditions, these values significantly decreased to 452±57 g/m2 and 31.6±1.4 g. The significant reduction in grain yield due to post-anthesis water stress might be due to a reduction in photo-assimilates production.

Effect of water stress on weed germination, growth characteristics, and seed production: a global meta-analysis

AbstractWeeds compete with crops for soil moisture, along with other resources, which can impact the germination, growth, and seed production of weeds; however, this impact has not been systematically recorded and synthesized across diverse studies. To address this knowledge gap, a global meta-analysis was conducted using 1,196 paired observations from 86 published articles assessing the effect of water stress on weed germination, growth characteristics, and seed production. These studies were conducted and published during 1970 through 2020 across four continents (Asia, Australia, Europe, and North America). Imposed water stress was expressed as solution osmotic potential (ψsolution), soil water potential (ψsoil), or soil moisture as percent field capacity. Meta-analysis revealed that water stress inhibits weed germination, growth, and seed production, and the quantitative response intensified with increasing water stress. A ψsolutiongreater than −0.8 MPa completely inhibits germination of both grass and broadleaf weeds. A ψsolutionfrom −0.09 to −0.32 MPa reduces weed germination by 50% compared with the unstressed condition. Moderate soil water stress, equivalent to 30% to 60% field capacity, inhibits growth characteristics (branches or tillers per plant, leaf area, leaves per plant, plant height, root, and shoot biomass) by 33% and weed seed production by 50%. Severe soil water stress, below 30% field capacity, inhibits weed growth by 51% and seed production by 88%. Although water stress inhibits weed growth, it does not entirely suppress the ability to germinate, grow, and produce seeds, resulting in weed seedbank accumulation. This creates management challenges for producers, because weed seeds can survive in the soil for many years, depending on weed species and environmental conditions. Quantitative information compiled in this meta-analysis can be instrumental to model the weeds’ multidimensional responses to water stress and designing integrated weed management strategies for reducing the weed seedbank.

Soil Microbiome Influences on Seedling Establishment and Growth of Prosopis chilensis and Prosopis tamarugo from Northern Chile.

Prosopis chilensis and Prosopis tamarugo, two woody legumes adapted to the arid regions of Chile, have a declining distribution due to the lack of new seedling establishment. This study investigated the potential of both species to establish in soil collected from four locations in Chile, within and outside the species distribution, and to assess the role of the root-colonizing microbiome in seedling establishment and growth. Seedling survival, height, and water potential were measured to assess establishment success and growth. 16S and ITS2 amplicon sequencing was used to characterize the composition of microbial communities from the different soils and to assess the ability of both Prosopis species to recruit bacteria and fungi from the different soils. Both species were established on three of the four soils. P. tamarugo seedlings showed significantly higher survival in foreign soils and maintained significantly higher water potential in Mediterranean soils. Amplicon sequencing showed that the four soils harbored distinct microbial communities. Root-associated microbial composition indicated that P. chilensis preferentially recruited mycorrhizal fungal partners while P. tamarugo recruited abundant bacteria with known salt-protective functions. Our results suggest that a combination of edaphic properties and microbial soil legacy are potential factors mediating the Prosopis establishment success in different soils.

Agar-based polyethylene glycol (PEG) infusion model for pea (<em>Pisum sativum</em> L.) — perspectives of translation to legume crop plants

Due to the oncoming climate changes water deficit represents one of the most important abiotic stressors which dramatically affects crop productivity worldwide. Because of their importance as the principal source of food protein, legumes attract a special interest of plant scientists. Moreover, legumes are involved in symbiotic association with rhizobial bacteria, which is morphologically localized to root nodules. These structures are critical for fixation of atmospheric nitrogen and highly sensitive to drought. Therefore, new drought-tolerant legume cultivars need to be developed to meet the growing food demand. However, this requires a comprehensive knowledge of the molecular mechanisms behind the plant stress response. To access these mechanisms, adequate and reliable drought stress models need to be established. The agar-based polyethylene glycol (PEG) infusion model allows a physiologically relevant reduction of soil water potential (Ψw), although it is restricted to seedlings and does not give access to proteomics and metabolomics studies. Earlier, we successfully overcame this limitation and optimized this model for mature Arabidopsis plants. Here we make the next step forward and address its application to one of the major crop legumes — pea. Using a broad panel of physiological and biochemical markers, we comprehensively prove the applicability of this setup to legumes. The patterns of drought-related physiological changes are well-interpretable and generally resemble the stress response of plants grown in soil-based stop-watering models. Thus, the proposed model can be efficiently used in the study of stress-related metabolic adjustment in green parts, roots and root nodules of juvenile and flowering plants.

The impact of phytochemical, morpho-physiological, and biochemical changes of Lallemantia royleana (Benth.) on drought tolerance

ABSTRACT Water deficiency is the most prominent constraint for crop production worldwide which is exacerbated by climate change. Developing drought-resistant species is a cost-effective solution to resolve the water lack problems in arid and semi-arid regions. A two-year study was conducted with the aim of developing the cultivation of Lallemantia royleana drought-resistant ecotypes in desert climates. Drought treatments were included control (−0.5 atm), mild (−3.5 atm), moderate (−6.5 atm), and severe (−9.5 atm). Balangu ecotypes were collected from Kalat in Khorasan Razavi province, Zakheh in Kurdistan province, Kondor in Alborz province, and Jupar in Kerman province. The results showed that Kondor and Jupar were drought-resistant ecotypes, and Kalat and Zakheh were drought-sensitive ecotypes. Growth traits, RWC, photosynthetic pigments content, seed yield, seed oil amount, and omega-6 fatty acids contents in all ecotypes decreased in drought conditions. On the contrary, the content of seed mucilage and soluble carbohydrates, the activity of APX, CAT, SOD, and POX, and the amount of phenol and proline increased. However, the drought-tolerant ecotypes produced more dry matter and seed yield under drought conditions. They can use a large amount of photosynthetic energy for biomass and seed production up to −6.5 atm of soil water potential. However, this ability is retained up to −3.5 atm of soil water potential in drought-sensitive ecotypes.

Hydraulic Sensitivity and Stomatal Regulation of Two Desert Riparian Species

AbstractCharacterizing plant response to water stresses is among the keys to understanding ecosystem functions. Despite increasing recognition of plant hydraulic and stomatal dynamics not captured by isohydricity, defined as the sensitivity of leaf water potential Ψl to soil water potential, it remains unclear which plant traits are critical to improved representation of plant hydraulic and stomatal dynamics beyond isohydricity, especially in dryland ecosystems. Here, we examine eco‐physiological responses of two typical desert riparian species, Populus euphratica and Tamarix ramosissima, to hydro‐meteorological variations. Based on measured hydraulic traits, variations of Ψl, leaf gas exchange, groundwater table, and soil moisture across vertical profiles, we investigated how subsurface hydraulic conditions control plant hydraulic sensitivity and stomatal regulation. We found both species exhibited anisohydric behaviors, which, however, were attributed to drying soil at different depths because of root distributions. The similar anisohydric behaviors also led to distinct stomatal regulation, due to the impact of atmospheric dryness decoupled from soil moisture and different sensitivities of stomatal conductance (gs) to Ψl. The latter was found to be dynamic throughout the growing season, which dominated the seasonal variation of gs and thus should not be neglected. The results suggest similar anisohydric behaviors could imply diverging hydraulic behaviors as the evaporate demand and flow regime change. Root morphological trait and stomatal sensitivity to Ψl are identified as keys to characterize responses to water stresses in desert riparian ecosystems. Our findings highlight that improved measurements and representations of these traits could contribute to better assessments of dryland ecosystem functions.

The quantitative importance of key root traits for radial water loss under low water potential

AimsRoot tissue water can be lost to the dry topsoil via radial water loss (RWL) resulting in root shrinking and loss of contact with the rhizosphere. The root barrier to radial oxygen loss (ROL) has been shown to restrict RWL, therefore we hypothesized that the inducible barrier can be formed as a response to low soil water potential and play a role, together with other root traits, in restricting RWL.MethodsRice and wheat were grown in hydroponics with contrasting water potential to diagnose ROL barrier formation and to explore how key root traits (ROL barrier, root diameter, root porosity) affect RWL. Moreover, we developed a numerical model predicting RWL as a function of root diameter, root porosity and presence of a barrier to ROL.ResultsMethylene blue staining showed that low water potential induced a ROL barrier formation in roots of rice, and also resulted in an apoplastic barrier, as identified by the apoplastic tracer periodic acid. The barrier significantly restricted RWL, but root diameter and tissue porosity also influenced RWL. Our numerical model was able to reflect the empirical data and clearly demonstrated that thick roots and a barrier to ROL restricts RWL while cortical porosity accelerates RWL.ConclusionsOur modelling approach highlighted that increase in root tissue porosity, a common response to drought, conserves water when new roots are formed, but the higher desiccation risk related to high-porosity roots can be effectively counteracted by forming thick roots or even better, by a barrier to ROL.